The findings of recent studies from both eastern and western Canada have shown that the drying behaviour of subalpine fir (A. lasiocarpa) and balsam fir (A. balsamea) is similar, which allows common solutions to be applied based on research conducted on one species of fir or the other. This article summarizes previous research findings and good practices that can be adopted in the short term to improve the drying of fir.
This study was conducted with the aim of assessing the effects of log storage time and conditions at a BC mill yard on veneer production under mill production conditions. The second objective was to validate the FPInnovations LogdryTM drying model for developed for wood piles in Eastern Canadian mills. The software was used to generate drying rate predictions under the BC mill’s prevailing weather conditions and storage times for comparison with some measured residual moisture contents of Douglas fir logs kept in storage at the mill for six and nine months, sampled and peeled in a laboratory trial in 2016.
The 2016 lab trials suggested little effect of lengthy (winter) storage up to 9 months but mill experience suggests this is excessively long and logs deteriorate in terms of veneer production and quality considerably earlier. Unfortunately due to experimental circumstances the mill peeling trials for the 9 month stored logs were unable to provide an accurate assessment of the true effect on production. Mills trials indicated % heavy sap had remained fairly stable largely within the mill target of 14% to 17% over the storage periods. During the mill trials there were unavoidable heavy confounding effects of different average diameter for log groups and peeler knife condition affecting the expected veneer production variables.
The trials also demonstrated how pile size and height play a major role in protecting logs from drying; with very dry logs having a deleterious effect on veneer production. Logs held in small piles for 12 months or more, even with artificial ‘drying retardants’ such as end sealant and tarping were too dry for reliable peeling, causing very rapid knife wear, spinouts, veneer break-up and line blockages and significant lost recovery. The % heavy sap offtakes from these trials were just 2% to 4%.
LogDryTM provides a fairly good estimate of likely drying rate trends of mid-sized (35 cm/14” to 41 cm/16” range) Douglas fir under the BC mills historic weather conditions over 6 and 9 months.
LogDryTM (Birch setting) was closest to measured log MC in large diameter (46 cm/18”) logs but the Aspen setting was closer to measured MC in small logs (<30 cm/12”). In the limited sample of logs available from the mill in 2016 the 12” logs were much drier after 9 months storage than the model predicted, even on the Aspen setting. Further sampling of piled logs in the small diameter range is needed to verify this observation.
LogDryTM was used to estimate drying rates of logs stored before or after Summer. Modelling indicated a shorter viable storage window for logs delivered before Summer compared to just before Winter, especially in the 6-month range. Residual log MCs were very similar after 12 months regardless of start time.
Further work is required to better calibrate LogdryTM for major Western Canadian species, particularly Douglas fir, Spruce and Lodgepole pine, and reduce the calculation time for simulations. Further adjustment may be needed for simulating real drying rates in very small logs. The model assumption of similar residual MC after 12 months regardless of start time also needs to be verified.
Des travaux récents tant dans l’est que dans l’ouest du Canada ont montré que le comportement au séchage du sapin subalpin (A. lasiocarpa) et du sapin baumier (A. balsamea) est similaire, ce qui permet une application de solutions communes à partir de travaux effectués sur l’une ou l’autre variété de sapin. Le présent
document se veut une revue sommaire de résultats de travaux antérieurs et de bonnes pratiques pouvant être adoptées à court terme pour améliorer le séchage de cette essence.